1. Field of the Invention
This invention relates to a precursor composition capable of forming a film of a polyimidesilicone resin at low temperatures within a short time.
2. Description of the Prior Art
As is known in the art, polyimide resins have wide utility in the fields of electronic industries since they have good heat resistance, mechanical strength and pattern forming properties and can be obtained as having a very high purity.
In general, however, polyimide resins are disadvantageous in poor adhesion to substrates such as silicon wafers. In order to improve the adhesion, attempts have been made to introduce siloxane bonds into a polyimide structure. For instance, U.S. Pat. Nos. 3,325,450 and 3,847,867 set forth processes for producing polyimides by reaction between diaminosiloxane used as a diamine component and a tetracarboxylic acid. Alternatively, Japanese Laid-open Patent Application No. 64-85220 and British Patent No. 2,168,065 set out processes for producing polyimides by reaction between a tetracarboxylic dianhydride having a siloxane bond and used as a tetracarboxylic acid component and a diamine component.
However, known polyimide resins having polysiloxane bonds in the backbone thereof are disadvantageously lower in heat resistance and mechanical characteristics than polysiloxane bond-free polyimides. If poly(siloxane-acid anhydride) wherein a number of dicarboxylic anhydride units are bonded to polysiloxane units is reacted with diamines in solutions to obtain polyimides, gelation is very likely to take place, making it difficult to obtain a polyimide with a uniform composition. Such a polyimide is not suited for surface protection such as of electronic parts.
Polyimide resins are insoluble in general-purpose organic solvents except for some high boiling solvents. In order to obtain a film of polyimide resin, it is usual to dissolve a polyamic acid, which is the precursor of a polyimide resin, in organic solvents and apply the resultant solution onto a substrate. The thus applied substrate is subjected to heat treatment at high temperatures over a prolonged time to remove the solvent and to cause ring-closure through dehydration thereby forming and curing a polyimide resin. However, the heat treatment under high temperature and prolonged time conditions is not advantageous from the standpoint of the production process. If the imidization does not proceed satisfactorily, the resultant cured film is impeded in physical properties. Accordingly, there is a demand for polyimide resins which are capable of being dissolved in solvents and being cured by heat treatment at low temperatures within a short time. However, when polyimides of the types which are soluble in organic solvents are dissolved in solvents, applied and cured, the resultant polyimide resin film is generally poor in solvent resistance.